With increasing development of science and technology, the functions and operating speeds of various electronic devices or mechanical systems are gradually enhanced. For maintaining normal operations, a forced convection mechanism (e.g. a fan) is installed in the electronic device or the mechanical system to dissipate heat that is generated by the electronic components of the electronic device or the mechanical system and maintain normal operating temperature. In view of power-saving efficacy, various electronic devices should have enhanced operating efficiency if the power consumption is fixed. For example, it is important to provide a fan having enhanced working efficiency in a power-saving manner.
FIG. 1 is a schematic top view illustrating an impeller of a fan according to the prior art. The impeller 1 comprises a hub 10 and a plurality of blades 11. The hub 10 is arranged at the center of the impeller 1. The blades 11 are disposed around the outer periphery of the hub 10. According to the practical requirements, the blades 11 have different profiles. For example, as shown in FIG. 1, the blades 11 are sweep-forward type blades.
As known, increasing the solidity of the blades 11 is a way of enhancing the working efficiency of the impeller 1. In the impeller 1, the ratio of the total area of the hub 10 and the blades 11 to the area of a circle whose radius R is from a center A to an outer periphery of the blades 11 is defined as the solidity. Moreover, for further increasing the working efficiency of the impeller 1, the blades 11 should be uniformly distributed. Since the length of the connecting end 111 and the stagger angle of each blade 11 are restricted by the perimeter of the hub 10, the number of blades 11 fails to be largely increased. Under this circumstance, the working efficiency of the impeller 1 is usually unsatisfactory.
Please refer to FIG. 1 again. There is a spacing interval B between every two adjacent blades 11. The spacing interval B between every two adjacent blades 11 at the outer peripheries of the blades 11 is wider than the spacing interval B between every two adjacent blades 11 near the hub 10. Under this circumstance, the number of blades 11 fails to be further increased, and thus it is difficult to effectively increase the solidity. Moreover, if large blades 11 are used to increase the solidity, every two adjacent blades 11 possibly overlap with each other. In this situation, the complexity of designing the mold of the impeller 1 and the fabricating cost of the impeller increases, and the performance of the fan deteriorates.